Litton Systems, Inc.

USA As Represented by Secretary of the Navy

Other

Bruce A Danver

A Douglas Meyer

Anthony Dandridge

Sandeep T Vohra

Alan B Tveten

Michael R Layton

Jeffrey D Lastofka

Eric Lee Goldner

Michael J Tweedy

Patrick J Welton

Gregory M Nau

Emery Moore

A pair of fiber optic coils are mounted on opposite sides of a flexural disk and are arranged to form an interferometer that produces an output signal in response to acceleration of the flexural disk. The flexural disk is mounted in a housing having first and second end plates with a sidewall extending between them. A support member extends between the end plates and through a central passage in the flexural disk. A pair of compressive dampers is mounted in the housing between the flexural disk and the housing end plates. A shear damper mounted on the central support member exerts a radial force on an inner edge of the central passage in flexural disk to dampen vibrations of the flexural member and control the output signal amplitude over a selected frequency range.

High performance fiber optic accelerometer

The interferometric fiber optic accelerometer is viewed as a mass-spring transducer housed in a sensor case. The sensor case is attached to a moving part whose motion is inferred from the relative motion between the mass and the sensor case. A flexural disk is housed in a sensor case which is accelerated in a direction normal to the plate surface. The plate undergoes displacement resulting in strains on the plate surface. A coil of optical fiber, made to be part of an optical interferometer, is attached to the flexural disk, the strain from the disk is transferred to the fiber thus changing the path length of the fiber interferometer. The interferometer output in demodulated providing the acceleration response. The design of the accelerometer housing is such that it is highly immune to extraneous signals, i.e., dynamic and hydrostatic pressure. Fabrication of the optical fiber coils is accomplished by winding the optical fiber, with a specially designed chuck to form reference and sensing fiber coils which are then bonded to the flexural disk to form the accelerometer.

Fiber optic accelerometer sensor and a method of constructing same

The interferometric fiber optic accelerometer is viewed as a mass-spring nsducer housed in a sensor case. The sensor case is attached to a moving part whose motion is inferred from the relative motion between the mass and the sensor case. A flexural disk is housed in a sensor case which is accelerated in a direction normal to the plate surface. The plate undergoes displacement resulting in strains on the plate surface. A coil of optical fiber, made to be part of an optical interferometer, is attached to the flexural disk, the strain from the disk is transferred to the fiber thus changing the path length of the fiber interferometer. The interferometer output in demodulated providing the acceleration response. The design of the accelerometer housing is such that it is highly immune to extraneous signals, i.e., dynamic and hydrostatic pressure. Fabrication of the optical fiber coils is accomplished by winding the optical fiber, with a specially designed chuck to form reference and sensing fiber coils which are then bonded to the flexural disk to form the accelerometer.

Apparatus for winding optic fiber coils

A plurality of air-backed elongate mandrels are arranged in an planar array such that their longitudinal axes are parallel. A length of a first optical fiber is wound around portions of each mandrel in a first group of the mandrels for exposure to the parameter. The first optical fiber is arranged such that exposing it to the parameter to be sensed causes the length of the first optical fiber to increase and decrease in direct proportion as the parameter increases and decreases. A length of the second optical fiber is wound around a second group of the mandrels for exposure to the parameter. The second optical fiber preferably is arranged such that exposing it to the parameter to be sensed causes the length of the second optical fiber to increase and decrease in inverse proportion as the parameter increases and decreases.

Fiber optic planar hydrophone

A fiber optic sensor is formed by providing a first mandrel section having a first longitudinal slot therein, placing a reference fiber within the slot and winding a sensing fiber around the first mandrel. The sensor includes a second mandrel section having a second longitudinal slot therein and a spacer between the first and second mandrel sections. The sensing fiber and the reference fibers are wound around the spacer, and then the reference fiber is placed in the second longitudinal slot. The sensing fiber is wound around the second mandrel section. The sensor may include additional mandrels and spacers to form additional sections. A plurality of sensing coils may be formed on each mandrel section.

Fiber optic sensor having mandrel wound reference and sensing arms

An acceleration insensitive interferometric hydrophone sensor having increased sensitivity comprises a rigid cylindrical support mandrel that is coaxial with and between thin walled sense and reference mandrels. Flanges on the reference and support mandrels form air filled cavities above and below optical reference and sense fiber windings, respectively, that are symmetrically wound on associated mandrels. The walls of the sense and reference mandrels are thin so that they both respond to the same incident acoustic wave signal although 180.degree. out-of-phase. A central collar on the support mandrel provides an acceleration insensitive location for making attachment to the hydrophone. In another embodiment, the reference mandrel is much thicker than the sense mandrel and cavities supporting the sense fiber are caused to operate as acoustic impedance mismatches for rendering the reference fiber winding substantially insensitive to and acoustically decoupling it from an incident acoustic pressure wave signal. In yet another embodiment which does not employ a reference mandrel, the reference fiber is wound around the support mandrel in cavities above the latter that are caused to operate as acoustic mismatches. The junctions of the mandrels are preferably sealed for isolating the wound length of reference fiber and cavities from fluid in which the hydrophone sensor is located.

High performance extended fiber optic hydrophone

An omnidirectional fiber optic hydrophone includes a concentrically-arranged pair of ring-shaped mandrels mounted between planar upper and base members. Each of the rings is formed of inner and outer annular portions separated by an annular void. Optical fibers wound about the outer circumference of the outer annular portion of the outer ring and about the outer circumference of the inner annular portion of the inner ring communicate with a source of optical energy and with a photodetector to provide signals for measuring acoustic wave-induced deflections of the rings. A plurality of mandrels may be employed in a single hydrophone which may be potted with elastomeric material or free flooded.

Omnidirectional fiber optic hydrophone

A mismatched path length fiber optic interferometer is optically coupled to an optical fiber and configured to form an omnidirectional acoustic sensor. A second mismatched path length fiber optic interferometer is optically coupled to the optical fiber and configured as a first gradient sensor. A second fiber optic gradient sensor is also optically coupled to the optical fiber. A detector optically coupled to the omnidirectional acoustic sensor and to the gradient sensors converts optical signals output therefrom to electrical signals indicative of the magnitude and direction of changes in an acoustic field. The omnidirectional acoustic sensor may include a length of optical fiber wrapped around the housing while the gradient sensors are mounted inside the housing. The housing perferably has a volume that is adjustable for controlling the buoyancy thereof. Each gradient sensor preferably comprises a pair of mandrels formed to enclose chambers. Optical fiber coils are formed on the mandrels. Both the chambers are filled with a fluid and placed in fluid communication through a tube that defines a sensing axis between the mandrels such that acceleration of the housing along the first sensing axis causes a fluid pressure differential on the first and second optical fiber coils.

Growing community of inventors

Tarzana, CA, United States of America

Bruce A Danver